Sometimes these are innocent, this may not be. I suspect at the moment then it is trying to find a vulnerability in an old version of WordPress. Of course, many people get WordPress installed by a web designer, or DIY, and forget about it. So there are many out-of-date versions on the Internet.

Come to think of it, Google Webmaster Tools even alerts its customers when it spots old software.

Anyway. Be careful, update your WordPress.

Just Googled [W1seb0x50] and it appears to be a typical (or atypical) attempt to access a computer by guessing the password. Odd that it comes up a few times.